US-2003/0090487 relates to a system and a method for providing a virtual tour, based on an organised set of still pictures. The system aims at giving a viewer the illusion of moving forward into the space depicted in a still picture.
US-2001/0034661 describes methods and systems for presenting a virtual representation of a real city. A user at a www client is enabled to navigate among interactive e-commerce items such as store fronts in a virtual city. The publication mainly relates to e-commerce aspects, and it apparently does not disclose a solution for virtual, continuous travelling in a virtual space defined by still pictures.